- 3 -
In the Altair Clone, data sent to the 88-LPC is transmitted out serial port
, which in turn, can be connected to a terminal emulator window to view
printer output, or connected directly to a serial printer. Normal serial port
functions of port still work when routing 88-LPC output through the port.
For example, serial port can be used as the cassette interface to load and
save programs and to also see line printer output.
If needed, the 88-LPC can be disabled if it interferes with your use of se-
rial port . See “Line Printer controller” in the “Administration Menu” sec-
tion of Part , “Configuration Monitor” for more information.
E. Floppy Drives
The Altair Clone provides three floppy “drives” that duplicate the function-
ality of the original Altair 8 inch floppy drives or the Altair Minidisk 5. 5
inch drive. Floppy storage is implemented using non-volatile RAM inside the
Altair Clone. Since physical floppy disks and drives are not present, “in-
serting” a floppy disk is done by uploading a floppy image from a PC to the
Clone. Conversely, a floppy image on the Clone can be saved back to a PC for
archiving.
Once uploaded to the Clone, floppy disk content is non-volatile and further
data exchange with a PC is not required to use the floppy drives. Floppy
disks can be swapped between the three drives (to put a different disk into
drive zero to boot, for example) without having to connect to a PC. The “Con-
figuration Monitor” makes floppy disk handling simple. See “Floppy Disk Menu”
in Part , “Configuration Monitor” for more information.
F. Interrupts and the 88-VI/RTC Board
Interrupts in the Altair 8800 Clone can be generated by the serial ports
( SIO and/or SIO for both transmit and receive), the floppy disk controller
("sector true" interrupt at the start of each sector), and by the real-time
clock present on the 88-VI/RTC board.
The 88-VI/RTC Vectored Interrupt/Real-Time Clock board prioritizes interrupts
to the 8080 processor from the vectored interrupt lines (VI0-VI7) on the Al-
tair bus. The board can also provide 60hz real-time clock interrupts. While
not widely used for most commercial software, the VI/RTC board is required by
MITS Time-Sharing BASIC for the Altair.
If the 88-VI/RTC board is not enabled, then the default interrupt structure
of the Altair (PINT with RST7) is used. In this case, all devices can be tied
into the PINT line at the same time as the emulated devices all drive the
PINT line with open collector outputs. As with the original hardware, all
boards (other than the 88-VI/RTC) ignore the 8080 interrupt acknowledge cy-
cle, so the 8080 processor sees a RST7 instruction on the bus (all data bits
high) during the interrupt acknowledge cycle.
Connection of device interrupt outputs to the desired vectored interrupt line
on the Altair bus (VI0-VI07) is done in the “Interrupt Vector Assignments”
menu of the “Administration Menu.” See these menus in Part , “Configuration
Monitor” for more information.
G. Changing Hardware Configuration
If an original Altair owner needed to install a new serial I/O card, install
or remove a PROM, or change a baud rate jumper, the owner opened the computer
and made the required modifications inside the computer. In the Altair 8800
Clone, these hardware configuration changes are made using menu options in
the “Configuration Monitor.” See Part , “Configuration Monitor” for more in-
formation.
